1. Field of the Invention
The present invention relates to a rearview mirror for indoor or outdoor use which is applied to a vehicle such as a car, and more particularly, to an electrochromic mirror in which the reflectivity can be changed by applying voltage.
2. Description of the Related Art
Conventionally, an “electrochromic mirror” is known (for instance, see Japanese Utility Model Application Publication (JP-Y) No. 62-2587). An electrochromic mirror may be used as a rearview mirror for a vehicle such as a car and can electrically change the reflectivity so as to reduce the glare of the headlight of a following car at night.
As shown in FIG. 2, in an electrochromic mirror 100 disclosed in JP-Y No. 62-2587, a transparent electrode 104, a thin film made of iridium hydroxide (Ir(OH)3) 106, a thin film made of tantalum pentoxide (Ta2O5) 108, a thin film made of tungsten trioxide (WO3) 110, and an aluminum (Al) electrode 112 are sequentially laminated on the back surface of a glass substrate 102 by vacuum deposition or the like. A glass plate 114 for protecting the thin films is adhered to the aluminum (Al) electrode 112 or the like by a sealant (adhesive) 116. When a voltage is applied between the transparent electrode 104 and the aluminum (Al) electrode 112 by a power supply 118, the thin film made of iridium hydroxide (Ir(OH)3) 106 and the thin film made of tungsten trioxide (WO3) 110 react to be colored, and the reflectivity of the electrochromic mirror 100 is changed (see arrow B shown in FIG. 2).
However, if the balance of the film thickness and film quality of each thin film described above is not kept in the electrochromic mirror 100, the thin film which becomes colored once may not return to its original state. In addition, problems exist in that stringent production conditions are required and the formation of a multi-layer film using vacuum deposition is expensive since any variation in the film thickness largely influences the performance.
On the other hand, an electrochromic mirror in which the reflectivity is changed by the coloring reaction of a so-called “electrochromic solution” which is a solution that is electrically colored is known (for instance, see Japanese Patent No. 2672083).
As shown in FIG. 3, in an electrochromic mirror 200 disclosed in Japanese Patent No. 2672083, two glass substrates 202 and 204 are arranged in parallel at a proper interval, and transparent electrode films 206 are respectively formed on the inner surfaces of the glass substrates 202 and 204. An electrochromic solution 210 is enclosed in a cell sealed by a sealant 208 between the transparent electrode films 206. A reflecting film 212 and a protective film 214 are formed on the back surface of the glass substrate 204 (the surface at the lower side in FIG. 3). When a voltage is applied between the transparent electrode films 206 by a power supply 216, the electrochromic solution 210 is colored, and the reflectivity of the electrochromic mirror 200 is changed.
However, when the two glass substrates 202,204 are not adhered together in parallel with a high precision via a sealant 208 in the electrochromic mirror 200, the image of the reflected light (see arrow C shown in FIG. 3) due to the reflecting film 212 does not coincide with that of the reflected light due to the surface of the glass substrate 202 (the surface at the upper side in FIG. 3). Therefore, so-called double images occur, and it is extremely difficult to see by using the mirror. In particular, since a mirror for a car is generally curved, a problem exists in that it is extremely difficult to manufacture the mirror, and thus the cost is high.
Therefore, there is a need in the art for an electrochromic mirror which can be easily manufactured at a low cost, causes no double images, and has a simple structure and high performance.